1. Field of the Invention
The present invention relates to an impact beam mounted in a car door and used for absorbing impact in the case of a collision and, more particularly, to an impact beam for car doors designed to have both an improved bending strength and an improved impact energy absorption capacity.
2. Description of the Prior Art
As well known to those skilled in the art, an impact beam is provided between the inside and outside panels of a car door for absorbing impact in the case of a collision. Conventional impact beams for car doors are made of steel pipes, and so they are undesirably heavy in weight and are somewhat inferior in their impact energy absorption capacity at a low temperature.
In an effort to compensate for such problems of conventional steel impact beams, a fiber reinforced impact beam, made of a fiber reinforced composite material having an improved specific strength (strength/density) and somewhat effectively absorbing impact energy, has been proposed and used.
Impact beams become most highly stressed at their central portions, when they are loaded with unexpected bending force. However, since the impact beams are conventionally designed to have a uniform thickness, they cannot effectively endure such bending force. In order to overcome such a problem, the impact beam may be designed to be increased in its thickness. However, such thick impact beams are problematic in that they undesirably waste material, and increase the production cost in addition to being heavy in weight.
Another problem experienced in the conventional impact beams resides in that the beam bracketing structure for fastening the impact beam to a support bracket of a door panel has been designed with only a consideration of strength while ignoring the impact energy absorption capacity.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an impact beam for car doors, which is reinforced at its central portion, and is improved in beam bracketing structure, thus being finally improved in bending strength and impact energy absorption capacity.
In order to accomplish the above object, the primary embodiment of the present invention provides an impact beam for car doors, comprising: a longitudinal beam stepped at two positions to allow its central portion to be thicker than its opposite end portions.
Another embodiment of this invention provides an impact beam, comprising: a longitudinal base beam body; and a hollow reinforcing beam body having a length shorter than that of the base beam body and a sectional size larger than that of the base beam body, and fitted over the central portion of the base beam body.
A further embodiment of the present invention provides an impact beam for car doors, comprising: a longitudinal beam; two support brackets fixedly mounted to a door panel; a fitting holder fixedly mounted at one end portion of each of the two support brackets to receive each end of the beam therein; and a locking bolt or a locking rivet used for locking the end portion of the beam to the fitting holder.